1. Field of the Invention
The present invention relates to an alumina sintered body and a method for producing the alumina sintered body.
2. Description of the Related Art
A computer, or an automatic control unit of an automobile or the like is equipped with a heat dissipation part for suppressing deterioration of performance due to an increase in heat generation amount which is associated with a large current. In recent years, a heat dissipation sintered substrate made of ceramic has received attention as a heat dissipation part in view of improving heat dissipation performance, productivity, production cost performance and so on.
Such a heat dissipation sintered substrate made of ceramic is required to have not only basic properties such as an electrical insulation property, but also a high heat conductivity and a high infrared ray emissivity from the viewpoint of heat dissipation. As a material of the heat dissipation sintered substrate, for example, aluminum nitride (AlN) has been heretofore used. However, the AlN heat dissipation substrate is significantly poor in water resistance, particularly chemical resistance to an alkali aqueous solution, and therefore has the problem that mounting of a circuit on the substrate is technically difficult. For example, the AlN heat dissipation substrate is required to be subjected to a surface treatment for imparting high chemical resistance by purposely oxidizing the surface layer to a depth of approximately several hundreds μm, so that production costs are increased.
Thus, a ceramic material to replace aluminum nitride, which has high chemical resistance while having a high insulation property, a high heat conductivity and a high infrared ray emissivity, is desired. Many of ceramic materials are prepared through a so called “sintering” process in which a raw material powder is fired to be solidified, and one of typical sintered bodies is an alumina sintered body. The alumina sintered body has a high insulation property and is excellent in chemical resistance.
It is known that properties which could not be exhibited by an alumina sintered body alone can be imparted to the alumina sintered body by selecting an additive to be used during sintering. For example, in Ando et al., “Material No. 52”, pages 1464 to 1470, published in 2003, it is reported that when silicon carbide is used as a sintering additive with alumina (Al2O3) used as a base material, a sintered body having a mechanical strength that is three times as high as that of conventional alumina alone is obtained.
However, an alumina sintered body that has been heretofore known is excellent in electrical insulation property and chemical resistance, but has a low heat conductivity and infrared ray emissivity. It is difficult to apply an alumina sintered body, which has a low heat conductivity and infrared ray emissivity, to a substrate of a heat dissipation part.
A ceramic material which has a high heat conductivity and a high infrared ray emissivity and is excellent in electrical insulation property and chemical resistance is desired as mentioned above, but one that satisfies all these properties and can be suitably used as a substrate of a heat dissipation part has not been found yet.
Under the above-mentioned circumstances, a main object of the present invention is to provide an alumina sintered body which has a high heat conductivity and a high infrared ray emissivity and is excellent in electrical insulation property and chemical resistance.